The recovery of plutonium from contaminated soils is made difficult by the lack of solubility of the plutonium in most aqueous media. Plutonium can become deposited in the soil due to leakage of nuclear waste containers, from scrapping operations of radioactive reactor cores from nuclear submarines, scrapping of nuclear weapons, from irradiated reactor fuels, atomic weapons testing, production of plutonium for nuclear weapons, and nuclear reactors that formerly produced plutonium.
The characterization of the chemical forms of plutonium present in the environment is still the object of intense research. Oxides and hydroxides appear to be representative and common constituents in the soil.
Current methods for the decontamination of soils and their attendant deficiencies are as follows: (1) Burial of wastes in depositories. The cost for transport and long-term storage of contaminated wastes are high and such containers often leak over the long term. (2) Solubilization of plutonium from soil using strong acids such as nitric or nitric/hydrofluoric acid. Such treatment is not practical due to corrosion problems and destruction of the soil matrix. (3) Use of siderophores or chelators alone to solubilize plutonium. Chelators such as EDTA solubilize only small quantities of plutonium. The most efficient siderophore studied thus far, (enterobactin), solubilizes only 20% of the plutonium in 6 days. (4) Volatilization of PuO.sub.2 as PuF.sub.6. Extremely high temperatures are required and fluorine gas is highly reactive and corrosive making this process expensive. There is no known prior art biological process for the microbial solubilization of plutonium.